This invention relates to a wet type sliding apparatus, more particularly to a wet type sliding apparatus comprising a wet type radial bearing excellent in wear resistance which bearing is used under high load conditions in the presence of a lubricating liquid (lubricating oil or lubricating water). Such a wet type sliding apparatus includes various ones such as generator, pump, marine engine and the like. This invention has improved such a wet type sliding apparatus by use of a radial bearing having a specific sliding surface.
As a material for the above radial bearing, there have heretofore been known white metal, a composite material of polytetrafluoroethylene (PTFE) and a glass fiber, polyethersulfone (PES) and the like.
Aromatic polyetherketone resins are known as engineering resins having excellent heat resistance, mechanical properties and wear resistance, and UK Patent No. 2,079,867 discloses a bearing in which polyetheretherketone (PEEK) is used as the sliding member.
However, the aromatic polyetherketone resin per se has a high friction coefficient, so that sliding members having a lower friction coefficient have heretofore been developed by using the aromatic polyetherketone resin as a base material and adding thereto a resin such as a fluorocarbon polymer or the like. On the other hand, however, this development results in a deterioration of wear resistance and mechanical strength because the fluorocarbon polymer is contained.
As a technique relating to these aromatic polyetherketone resins, the technique disclosed in JP-A 58 (1983)-160,346 is known though it relates to a dry type sliding member.
In this prior technique, as a sliding member of a dry type sliding apparatus in which no lubricating liquid is used, there is stated a resin composition comprising a thermoplastic aromatic polyetherketone resin as a base material, 2.5 to 60% by weight of a polytetrafluoroethylene (PTFE) and 2.5 to 60% by weight of a carbon fiber. However, the composition range in which the practical heat distortion temperature (HDT) and limiting PV value have been actually confirmed is only 10 to 40% by weight of a fluorocarbon polymer (polytetrafluoroethylene) and 10 to 40% by weight of a carbon fiber. When a composition of 2% by weight of a fluorocarbon polymer and 18% by weight of a carbon fiber is used in the bearing of a copying machine, it has been confirmed that a creak is generated and the revolution becomes unusual (see Comparative Example 3 in the above prior art reference), and it is suggested that the amount of the fluorocarbon polymer becoming small is not desirable.
Moreover, polyarylene sulfide resins are known as engineering resins excellent in heat resistance, mechanical properties and wear resistance. However, similarly to the aromatic polyetherketone resins, the polyarylene sulfide resins per se have a high friction coefficient and have been considered to be difficult to apply to a sliding member.
Recently, the area of the sliding surface of a radial bearing which starts in the presence of a lubricating liquid and which is incorporated into an apparatus such as a generator, a pump or the like, has been made small accompanying the tendency of miniaturization of the apparatus, and a higher surface pressure has come to apply to the sliding surface. The radial bearing which is applied under such severe conditions has been required to have wear resistance in addition to excellent sliding characteristics under wet lubrication. Furthermore, in the case of the wet type radial bearing in which starting and stopping are repeatedly effected, only a small amount of a lubricating liquid is present at the time of the starting and the sliding surface of the bearing is partially in solid contact, so that not only does a large starting power become necessary, but also, there is a fear that the sliding surface is damaged by the solid contact. Therefore, in addition to the wear resistance during the operation, it is required that the friction coefficient at the time of the starting should be small. The wear resistance in the wet type system should be such that the wear is 4 .mu.m or less, particularly preferably 2 .mu.m or less as determined by a change in thickness of test sample before and after a test in which a counter member is rotated for 30 seconds in an oil bath by, for example, a friction and wear testing machine and then stopped for 300 seconds and this cycle is repeated 15 times (see Table 7 which appears hereinafter).
However, in the case of a sliding member in which white metal is used, a damage by solid contact tends to be caused at the time of the starting, and in the case of a sliding member in which PES is used, there has such a problem that it tends to be deteriorated by reaction with a lubricating oil and is lacking in durability. Moreover, a sliding member consisting of a composite material of PTFE and a glass fiber has such a problem that the mechanical strength is small and distortion tends to be caused.
In addition, the wear resistance and mechanical properties stated as to 10 to 40% by weight of a fluorocarbon polymer (polytetrafluoroethylene) and 10 to 40% by weight of a carbon fiber which are the ranges of the best mode of the above-mentioned prior art relating to the dry type technique have not been said to be sufficient. Moreover, as discussed above, in Comparative Example 3 of the above-mentioned prior art reference, it has been confirmed that when a composition consisting of 2% by weight of a fluorocarbon polymer and 18% by weight of a carbon fiber is used in the bearing of a copying machine, a creak is generated and the rotation becomes unusual, and it is stated that when the amount of the fluorocarbon polymer is 2% by weight, the composition is inappropriate as a sliding member. Furthermore, in the dry type prior technique, when the amount of PTFE is less than 10% by weight, no sufficient lubricity is actually obtained.